Field of the Invention
The invention relates in general to a semiconductor device and a compensation method therefore.
Description of the Related Art
Semiconductor memory devices are important in modern electronic devices. Semiconductor memory devices have many types. Resistance change memory device is one of the types of the semiconductor memory devices. Resistance change memory device includes phase change memory (PCM) device and transition metal oxide (TMO) resistive memory. Data storage into the resistance change memory device is achieved by changing the resistance of the resistance change memory device.
The resistance of the resistance change memory device is a temperature function. That is, the resistance of the resistance change memory device is affected by the temperature of the memory device.
Usually, if the device temperature is high, the sensing window of the resistance change memory device may be reduced. As for the resistance distribution of a plurality of memory cells, at high temperature, the sensing window may even disappear, which results in read fail.
FIG. 1 (prior art) shows a relationship between resistance and temperature in applying a fixed reading bias voltage, wherein the reference resistance level is fixed. If the resistance is higher than the reference resistance level, then the memory cell is determined to be at a high resistance state, for example, a reset state. The high resistance state refers to that the memory cell stores logic 1. On the contrary, if the resistance is lower than the reference resistance level, then the memory cell is determined to be at a low resistance state, for example, a set state. The low resistance state refers to that the memory cell stores logic 0.
The sensing window exists between the high resistance state and the low resistance state. As shown in FIG. 1, if the temperature is high, the sensing window may be narrow. If the temperature is higher than the temperature threshold T1, data reading is failed. The reason is as follows. In sensing the memory cell which had been programmed as high resistance state, the sensed resistance of the memory cell is lower than the reference resistance level if the temperature is over the temperature threshold T1. Therefore, the memory cell is mistakenly determined as low resistance state.
FIG. 2 (prior art) shows the resistance-temperature relationship by applying a fixed reading bias voltage, wherein the reference state level is tracking. The tracking reference state level may track the high resistance state and the low resistance state. However, if the temperature is high, the high resistance state and the low resistance state will be overlapped and thus the reading is failed.
Another characteristic of the resistance change memory device is that, the resistance is a function of the reading bias voltage. That is, the resistance thereof is related to the applied reading bias voltage. FIG. 3 (prior art) shows the resistance of the resistance change memory device and the applied reading bias voltage under fixed temperature. At the same temperature, if the applied reading bias voltage is lower, the resistance is higher; and vice versa.
The application discloses a semiconductor device and a compensation method therefore, which compensates negative effects by considering the relationship between the resistance and the temperature, and the relationship between the resistance and the reading bias voltage.